* fix#6228: do not display eth price in cli for etc
Current behaviour:
When the client is started with defaults, the miner's gas calibrator
periodically queries the price of ether in usd and uses it to adjust
the wei_per_gas variable, displaying an info message in the cli each
time calibration happens. The info message mentions the price of ETH.
When started with the --min-gas-price option, the calibrator is inactive
and the price is not displayed.
Problem:
When running on an alternate chain such as ethereum classic, the info
message mentioning the ETH price is present, unless the --min-gas-price
option is used.
Solution:
if chain != foundation and --min-gas-price is not set,
don't use GasPricerConfig::Calibrated as default but rather fix
the minimum gas price to zero.
* self.chain() returns ChainType.
* match chain based on SpecType